This invention relates to a composition and method for generating self-destructing filter cakes in wellbores and in subterranean formations. More particularly it relates to a composition and method for injection of solids-containing fluids that form filter cakes in which acids are generated after the filter cakes have been placed. Finally, it relates to using the composition and method in oilfield applications.
There are many oilfield applications in which filter cakes are needed in the wellbore, in the near-wellbore region or in one or more strata of the formation. Such applications are those in which without a filter cake fluid would leak off into porous rock at an undesirable rate during a well treatment. Such treatments include drilling, drill-in, completion, stimulation (for example, hydraulic fracturing or matrix dissolution), sand control (for example gravel packing, frac-packing, and sand consolidation), diversion, scale control, water control, and others. Typically, after these treatments have been completed the continued presence of the filter cake is undesirable or unacceptable.
Solid, insoluble, materials (that may be called fluid loss additives and filter cake components) are typically added to the fluids used in these treatments to form the filter cakes, although sometimes soluble (or at least highly dispersed) components of the fluids (such as polymers or crosslinked polymers) may form the filter cakes. Removal of the filter cake is typically accomplished either by a mechanical means (scraping, jetting, or the like), by subsequent addition of a fluid containing an agent (such as an acid, a base, or an enzyme) that dissolves at least a portion of the filter cake, or by manipulation of the physical state of the filter cake (by emulsion inversion, for example). These removal methods usually require a tool or addition of another fluid (for example to change the pH or to add a chemical). This can sometimes be done in the wellbore but normally cannot be done in a proppant or gravel pack. Sometimes the operator may rely on the flow of produced fluids (which will be in the opposite direction from the flow of the fluid when the filter cake was laid down) to loosen the filter cake or to dissolve the filter cake (for example if it is a soluble salt). However, these methods require fluid flow and often result in slow or incomplete filter cake removal. Sometimes a breaker can be incorporated in the filter cake but these must normally be delayed (for example by esterification or encapsulation) and they are often expensive and/or difficult to place and/or difficult to trigger.
There is a need for a new composition and method in which a filter cake is formed from at least two components, one of which slowly reacts with water, and the second of which reacts with a reaction product of the first to destroy the filter cake spontaneously.